This invention relates, in general, to mold assemblies, and more particularly, to a method of using a molding assembly wherein its molding pot has a configured bottom.
Molding assemblies have been used for some time to encapsulate semiconductor devices. A molding assembly typically has a plurality of cavities in which the device being encapsulated is located. A receptacle commonly called a pot is located on the molding assembly to receive the encapsulating material. Some molding assemblies have more than one pot. Runners connect the cavities to the molding pot. A plunger or ram is used to force the encapsulating material in the pot into the runners and into the cavities. Typically the molding assembly is heated to a temperature which will cure the encapsulating material. The encapsulating material is generally a thermoset epoxy which cures at approximately 170.degree. C.
Although this type of a molding apparatus works reasonably well, some shortcomings do exist. As an example, during encapsulation the encapsulating material can cause the thin connecting wires on the semiconductor device to be dislodged, which is commonly referred to as wire sweep. In addition, voids can occur in the encapsulating material itself, thereby not providing ideal encapsulation. It appears that the dislodging of the fine wires is a result of the failure of the encapsulating material to be sufficiently fluidized during injection into the cavity. Another cause may be that the encapsulating material is injected under too high of a pressure. It is believed that the voids are sometimes caused by the lack of fluidization of the encapsulating material, or by a chase or runner jamming mechanism which occurs when the encapsulating material starts to solidify before it reaches the desired voids in the cavity. As additional encapsulating material is forced down the runners the partially solidified material enters the cavity but fails to completely fill the cavity. Multi-pot molds have been used in an attempt to overcome some of the problems of a single-pot mold; however, very high pressures are required in order to obtain a good encapsulation. By now it should be appreciated that it would be desirable to have an improved molding apparatus and method of encapsulation.
Accordingly, it is an object of the present invention to provide an improved molding assembly and method of use.
Another object of the present invention is to provide a method of using a molding assembly wherein the pot has a configured bottom.
Yet another object of the present invention is to use a molding assembly which will result in a superior encapsulation at lower pressures.
Yet another object of the present invention is to provide a method for using an improved molding pot which results in a better fluidization of an unheated encapsulating material pellet.